diff --git a/crates/border-wars/src/hex.rs b/crates/border-wars/src/hex.rs
index 0f9aa3a..b02c530 100644
--- a/crates/border-wars/src/hex.rs
+++ b/crates/border-wars/src/hex.rs
@@ -8,8 +8,8 @@ use num::Signed;
 use partial_min_max::{max, min};
 
 /// Represents a number that can be used in a hexagonal grid.
-pub trait HexNumber: Signed + PartialEq + Copy + PartialOrd {}
-impl<T: Signed + PartialEq + Copy + PartialOrd> HexNumber for T {}
+pub trait HexNumber: Signed + PartialEq + Copy + PartialOrd + FromPrimitive {}
+impl<T: Signed + PartialEq + Copy + PartialOrd + FromPrimitive> HexNumber for T {}
 
 /// Represents a position in a hexagonal grid.
 /// We use the axial coordinate system explained in this